/usr/lib/x86_64-linux-gnu/libOTBTestKernel-5.8.so is in libotb-dev 5.8.0+dfsg-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libOTBTestKernel-5.8.so.1
/usr/lib/x86_64-linux-gnu/libOTBTestKernel-5.8.so.1